Conversion (Electrical Power Toolkit)

A delta to wye (D to Y) conversion converts a line voltage to a phase voltage. You use a D to Y conversion when you calculate power, impedance, and signaling voltage, which are always phase-based no matter what the connection is. However, a D to Y conversion is useful only when a three-phase electrical power system is symmetric. Otherwise the values from the conversion do not correspond to actual phase values.

A wye to delta (Y to D) conversion converts a phase voltage to a line voltage. In some high-voltage systems, you can specify the nominal voltage as the line voltage because a high-voltage system is usually isolated and there is no neutral wire. However, sometimes voltage transformers have connections that produce phase voltage on the output. The output phase voltage returns precise information about the phase on which the disturbance occurs. On the line voltage side you have voltages from two phases combined so that you do not directly see voltage fluctuations on individual phases. Thus you perform a Y to D conversion when you have phase voltage outputs from voltage transformers but the high-voltage side connects to delta.